This invention relates to an improved bearing assembly for transmission shafts. Specifically, the invention relates to an improved bearing assembly that compensates for the increase in shaft end play caused by rising temperature during operation of the transmission.
Prior art transmissions typically have main and auxiliary countershafts coupled to transmission input and output shafts by ears to achieve a desired multiplication of torque. The countershafts are supported within a transmission housing by bearing assemblies. The bearing assemblies are arranged between the housing and the ends of the shafts to minimize the friction between the housing and shafts as the shafts rotate about their axes.
Under certain operating conditions the shafts may have some end play. That is, the shafts have clearance within bearing assemblies that permits slight movement along their axes relative to the housing. The bearing assemblies are designed primarily to withstand large radial loads but only minimal axial loads. As a result excessive end play, which permits higher axial loads, may increase bearing wear and noise. In an effort to minimize end play, the bearings are typically axially located and shimmed during installation to achieve a desired axial clearance or tolerance.
Typically, the bearing assemblies are press fit, or permanently affixed, into housing openings and onto the ends of the shafts. As a result, the desired axial tolerance cannot be adjusted as the amount of end play changes during the course of transmission operation. Specifically, as the transmission temperature changes, the transmission components expand and contract as the temperature rises and falls, respectively. This situation is complicated by the fact that the transmission components are constructed from different materials having different coefficients of thermal expansion. For example, the housing is constructed from aluminum, which has a high coefficient of expansion, while the bearings and shafts are constructed from steel, which have a low coefficient of thermal expansion. Since, at the same temperature, the housing expands more than the bearings and shafts, end play may increase as the temperature rises.